1. Technical Field
The present invention relates to a heat-dissipating substrate and a fabricating method thereof.
2. Description of the Related Art
Today, as electronic parts are seeking miniaturization, thinness, and high density and as such become light, thin, short and small, the miniaturization, micro patterning and packaging of a Printed Circuit Board (PCB) are being carried out with these things being taken into consideration. Thus, the PCB is more complicated in structure and the mounting density of parts is increased.
However, as the number and density of electronic parts mounted on the PCB increase, measures are required to provide for the dissipation of heat generated from the electronic parts and to prevent warpage.
In order to solve the problems presented by heat dissipation and warpage, a variety of types of package substrates have been proposed. However, the package substrate may be deformed because of residual stress resulting from a difference in a thermal expansion coefficient between a semiconductor chip, underfill and a substrate and a thermal cycle during a fabrication process. Thus, a structure for minimizing deformation using a metal core which is low in thermal expansion coefficient and for solving the problems of warpage and heat dissipation has been proposed.
FIGS. 1 to 5 are sectional views illustrating a conventional fabricating method of a PCB using a metal core. The fabricating method will be described with reference to the accompanying drawings.
First, a metal core 11 having high heat conductivity is prepared (see FIG. 1).
Next, through holes 12 are formed in the metal core 11 through drilling or etching (see FIG. 2).
Subsequently, insulating layers 13 are formed on both sides of the metal core 11 including the through holes 12 (see FIG. 3).
Next, for layer-by-layer connection, the through holes 12 of the metal core 11 are mechanically machined, thus forming via holes 14. Here, the via holes 14 are machined to be smaller than the through holes 12 of the metal core 11 to be insulated from a copper plating layer formed on the inner wall of each via hole 14 through a subsequent copper plating process (see FIG. 4).
Thereafter, the copper plating layer is formed on the surface of each insulating layer 13 and the inner wall of each via hole 14 through chemical copper plating, that is, electroless plating and electrolytic plating. Through exposing, developing and etching processes, circuit layers 15 are formed. In this way, a PCB 10 is fabricated.
However, the conventional fabricating method of the metal core heat-dissipating substrate 10 has the following problems.
First, in order to prevent electric failure due to a short occurring in the plating layer formed on the metal core 11 and the inner wall of each via hole 14, the through holes 12 must be machined to a sufficient size. In this case, the ratio of the remaining metal core for a substrate area is only about 50%, so that heat conductivity is reduced.
In order to increase heat dissipation efficiency, the metal core 11 is inserted. However, this increases the overall thickness of the substrate. Since the insulating layer 13 such as a prepreg which is very low in heat conductivity is used, the heat conducting effect of the metal core is deteriorated.
In order to solve the problems, the structure of an anodized metal substrate 50 shown in FIG. 6 has been proposed. According to this structure, an anodized layer 54 is formed on a surface of the metal plate 52, and a circuit layer 56 is formed on the anodized layer 54.
The anodized metal substrate 50 is superior to the metal core heat-dissipating substrate 10 in heat dissipation performance. However, the anodized metal substrate 50 is problematic in that, when a device susceptible to heat is mounted on the circuit layer 56, heat conduction is performed and thermal isolation is not performed, so that the device susceptible to heat may be damaged.